add fixed-length lists

docs/language/lists.md

@@ -21,6 +21,24 @@ list point points; # empty list of points.
 list point points = [100, 200, 300, 400]; # points[1] == point {x: 100, y: 200} and so on...
 ```
 
+### With a fixed length
+
+Use `[value; length]` to make a list whose items all start with the same value.
+
+```goboscript
+list scores = [0; 1000]; # 1,000 items, all set to 0.
+list names = [""; 25]; # 25 empty strings.
+```
+
+This form also works with struct lists. The starting value is used for each field.
+
+```goboscript
+struct point {x, y}
+list point points = [0; 100]; # 100 points whose x and y fields are both 0.
+```
+
+The length cannot be negative, infinite, `NaN`, or greater than 200,000.
+
 ### Read contents from a text file
 
 This allows you to load a text file line-by-line into a list of strings.
@@ -123,4 +141,3 @@ value = list_name["last"];
 | `list_name[index] //= y;` | ![](../assets/list_floor_divide.png){width="400"} |
 | `list_name[index] %= y;` | ![](../assets/list_mod.png){width="400"} |
 | `list_name[index] &= y;` | ![](../assets/list_join.png){width="400"} |
-

src/ast/list.rs

@@ -23,6 +23,7 @@ pub struct List {
 pub enum ListDefault {
     Values(Vec<ConstExpr>),
     File { path: SmolStr, span: Span },
+    FixedLength(ConstExpr, ConstExpr),
 }
 
 impl List {
@@ -63,4 +64,20 @@ impl List {
             is_used: false,
         }
     }
+
+    pub fn new_fixed_length(
+        name: SmolStr,
+        span: Span,
+        type_: Type,
+        default: ConstExpr,
+        length: ConstExpr,
+    ) -> Self {
+        Self {
+            name,
+            span,
+            type_,
+            default: Some(ListDefault::FixedLength(default, length)),
+            is_used: false,
+        }
+    }
 }

src/codegen/sb3.rs

@@ -938,6 +938,22 @@ where T: Write + Seek
                     vec![]
                 }
             },
+            Some(ListDefault::FixedLength(value, length)) => {
+                let multiplier = list
+                    .type_
+                    .struct_()
+                    .and_then(|(struct_name, _)| s.get_struct(struct_name))
+                    .map(|struct_| struct_.fields.len())
+                    .unwrap_or(1);
+                let value = s.evaluate_const_expr(d, value);
+                let len = s.evaluate_const_expr(d, length).to_number();
+                if len > 200_00_f64 || len.is_nan() || len.is_infinite() || len < 0_f64 {
+                    d.report(DiagnosticKind::FixedLengthListInvalid(len), &length.span());
+                    vec![]
+                } else {
+                    vec![value; len as usize * multiplier]
+                }
+            }
             None => vec![],
         };
         match &list.type_ {

src/diagnostic/diagnostic_kind.rs

@@ -10,6 +10,7 @@ use crate::{
     ast::{
         Sprite,
         Type,
+        Value,
     },
     blocks::{
         Block,
@@ -127,6 +128,7 @@ pub enum DiagnosticKind {
     UnusedFunc(SmolStr),
     UnusedArg(SmolStr),
     UnusedStructField(SmolStr),
+    FixedLengthListInvalid(f64),
 }
 
 impl DiagnosticKind {
@@ -298,6 +300,21 @@ impl DiagnosticKind {
                 format!("duplicate variant {variant_name} in enum {enum_name}")
             }
             DiagnosticKind::EmptyStruct(name) => format!("struct {name} is empty"),
+            DiagnosticKind::FixedLengthListInvalid(value) => {
+                if *value < 0_f64 {
+                    return format!("list length cannot be negative");
+                }
+                if value.is_infinite() {
+                    return format!("list length cannot be infinite");
+                }
+                if value.is_nan() {
+                    return format!("list length cannot be nan");
+                }
+                if *value > 200_000_f64 {
+                    return format!("list length cannot be greater than 200,000");
+                }
+                unreachable!()
+            }
         }
     }
 
@@ -485,6 +502,7 @@ impl From<&DiagnosticKind> for Level {
             | DiagnosticKind::InvalidCostumeFormat { .. }
             | DiagnosticKind::InvalidSoundFormat { .. }
             | DiagnosticKind::LocalNotSupported
+            | DiagnosticKind::FixedLengthListInvalid(..)
             | DiagnosticKind::UnknownDirective(_) => Level::Error,
 
             | DiagnosticKind::FollowedByUnreachableCode

src/parser/grammar.lalrpop

@@ -89,6 +89,9 @@ Declr: () = {
     LIST <type_:Type> <l:@L> <name:NAME> <r:@R> <pl:@L> <path:STR> <pr:@R> ";" => {
         sprite.add_list(List::new_file(name, l..r, type_, path, pl..pr), diagnostics);
     },
+    LIST <type_:Type> <l:@L> <name:NAME> <r:@R> "=" "[" <default:ConstExpr> ";" <length:ConstExpr> "]" ";" => {
+        sprite.add_list(List::new_fixed_length(name, l..r, type_, default, length), diagnostics);
+    }
 }
 
 EnumVariant: EnumVariant = {